Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of the common general knowledge in the field.
In several geographies water shortage is becoming a more and more acute problem and this is particularly true in developing countries.
Household cleaning processes like washing laundry, dishes etc, require large amounts of water. It will be a great benefit to the society if it will be possible to save this water and also reuse the water used in such activities. The water generated in-home from washing and rinsing laundry is generally referred to as grey water. In order to reuse such household grey water for various activities it is essential to remove all the particulate matter and the surfactants.
Several water purification processes using chemicals such as flocculants and coagulants especially for making water safe for drinking are known in the art. There are also several techniques to purify industrial waste water. Most of these methods involve use of chemicals like aluminium salts and polymers which have an adverse effect on the environment.
WO2002000557 (P&G) describes a water purification composition comprising essentially a primary coagulant, a bridging flocculent, a coagulant aid and optionally a disinfectant. This patent application also claims a method for clarifying and purifying water, which comprises several stages selected from coagulation and flocculation, disinfection, filtration, neutralisation and fortification.
EP1953119 (Unilever) describes solid water purification composition in the form of a two-component system, with a first component comprising a biocide and a water-insoluble adsorbent, and a second component comprising a coagulating agent and a flocculating agent. A biocide quencher may be included in the composition.
WO2012084621 (Unilever), discloses a fast water purification and clarification process for the treatment of household water, especially laundry wash and more typically laundry rinse water by using a composition comprising flocculant, coagulant, filler and cationic surfactant, effective for water clarification and purification.
WO15003009 (Aquacache Inc) discloses a method for treating wastewater containing solid materials and one or more of fats, oils and grease which comprises simultaneously subjecting water to be treated to sparging air in the presence of singlet oxygen and/or hydrogen peroxide. The method for purifying grey water is by using advanced oxidation to degrade the organics and surfactants. The singlet oxygen is generated by a reaction of hydrogen peroxide and sodium hypochlorite. The aeration produces foam, which is used to remove the solids, fats and oily soils by a method similar to froth flotation. The foam is handled/broken by using vacuum. The method is very elaborate and involves the use of many difficult to handle chemicals and does not teach how to recover the surfactants from grey water but would actually be degrading the organics and surfactants.
US201331994 (Nexus Ewater) discloses to a process and apparatus that treats waste water, in particular waste water containing surfactants and including grey water, for local reuse. In this process a gas is used to treat the waste water which leads to the generation of bubbles. The bubbles are moved to a “separating chamber”, from which some liquid may further drain out. This liquid is recycled to the main waste water containing chamber. Water treatment occurs by coarse filtration (>200 microns), adsorptive filtration and UV treatment. The gas used for generating the bubbles is air or ozone, which is claimed to be generated by exposing the waste water to UV light. The Gas injection rate is 1 to 4 LPM. Activated carbon filters are used for adsorptive removal of residual surfactants from the waste water.
The foam is generated at a very low rate (1 to 4 LPM), and the bubbles are separated out in a separate chamber for drying. This would require a lot of space, especially for treating high surfactant concentrations in grey water in an in-home device such as a washing machine. It does not disclose how surfactant can be recovered from the foam in a continuous high speed operation. The use of ozone shows that chemical degradation of the surfactant is desired, by oxidation, and no surfactant recovery is mentioned.
A device and a process for purification of grey water, especially grey water generated in household processes such as laundry wash and rinse water without the addition of chemicals is highly desired and is beneficial to the environment.
Goldberg and Rubin (I & EC Process Design and Development, 1967, Vol 6) disclose process of mechanical foam breaking by the shearing action of a high speed rotating disc. However it only discloses foam flow rates upto 200 ml/min by using a smooth disc rotating at a speed of about 2500 rpm. The surfactant used in the process was Triton X-100 which is not a very high foaming surfactant and at relatively low concentrations. They also had a limitation on the disc speed and aeration rate because of which there was increased amount of liquid carried with the foam. They do not disclose how to recover purified water or surfactant concentrate from grey water.
Andou S et al., (Performance characteristics of mechanical foam breakers with rotating parts fitted to bubble column, J. of chem. tech. and biotech, vol 68, no. 1, 1 Jan., 1997, pg 94-100), compares mechanical foam breakers shaped like fans with vanes/blades oriented perpendicular to the plane rotation with the “blades” in various orientations. These foam breakers, not only consume more power, but also cause a fine mist of droplets in the exhaust air and the liquid phase of the foam gets scattered into a mist which is carried with the air-flow stream leaving the foam breaker. Thus the recovery and collection of pure water from grey water is low.
Our co-pending application EP13187691 discloses a device and a physical process for purification of grey water especially for in-home purification, which process does not require the addition of chemicals. It was found that it was possible to design a device and a process where, by continuous aeration, more than 90% of the surfactant present in used laundry water can be transferred into foam. If the foam was then allowed to channel out from the chamber holding the grey water, and made to collapse outside the chamber, a device and process could be built to remove dissolved surfactants from water. It was thus possible to recover more than 90% of grey water as purified water even when the surfactant level in the grey water was as high as 0.1%. The recovered purified water preferably could be subsequently passed through at least one filter to get further purified water. The key step in achieving the above was the ability to cause foam collapse at very high volumetric flow rate of the foam.
The process and device disclosed in EP13187691 is capable of recovering pure water from laundry waste water by concentrating the dirt and the surfactants present in laundry waste water, as a “reject” which is around 10% of the volume of the initial laundry waste water. Since the dirt and oily soils from the laundry process are mixed with these surfactants from the laundry products in this concentrated waste stream, this reject liquid has to be discarded. This concentrated reject is both a burden on the environment as well as a loss of surfactants which could be reused. It would be highly beneficial, if a clean surfactant solution could be extracted from this “dirt” containing surfactant concentrate reject.
In addition to the above, the presence of oily soil and dirt particles present in laundry waste waters interfere with the foam generation in the aeration step. This leads to sub-optimal removal of the surface active agents from the laundry waste water by aeration and foam collapse. Hence it would be beneficial to design a device and a method which ensures efficient removal of surfactant from the laundry waste water, irrespective of the quantity and type of soils present in the laundry waste water.
It has now been found that if the laundry wash liquor is passed through an ultra filter capable of removing dirt and oily soils present in laundry waste water prior to the aeration and foam breaking it is possible to get a surfactant rich concentrate from the collapsed foam, purified water and a reject containing the particulate and oily soil. It is thus possible to recover up to 70% of the initial surfactant in the wash liquor as a liquid concentrate and up to 90% of the laundry waste water as the purified water.
It is an object of the present invention to provide a device for recovery of surfactant concentrate and purified water by purification of grey water generated in household process, especially laundry wash and rinse processes without the addition of chemicals that have an adverse effect on the environment.
It is another object of the present invention to provide a device for recovery of surfactant concentrate and purified water where the surfactant level of the grey water is reduced to less than 1 ppm.
It is another object of the invention to provide a simple physical process for purification of grey water where 70% of the surfactant is recovered as surfactant concentrate and more than 90% recovery of purified water can be achieved.